Graphite resistor



Patented a. 19, 1937 PATENT OFFICE GRAPHITE RESISTOR Robert E. Gould,Norris, Tenn.

No Drawing. Application July 27, 1936, Serial No. 92,945

9 Claims.

(Granted under the act of March 3, 1883, as amended April 30, 1928; 3700. G. 757) This application is made under the act of March 3, 1883, asamended by the act of April 30, 1928, and the invention hereindescribed, if patented, may be manufactured and used by or for theGovernment for governmental purposes without the payment to me of anyroyalty thereon.

This invention relates to a process for sealing a graphite resistor in arefractory protection tube.

One of the objects of this invention is to increase the life of graphiteresistors in high temperature furnaces. Another object of this inventionis to provide a means for the exclusion of oxygen from contact withgraphite resistors operating at high temperatures. Other objects of thisinvention include the provision of an economical and effective means forsealing graphite resistor assembly units. 20 I have discovered a processfor effectively completing the manufacture of high temperature graphiteresistor units by introducing a gas, liquid or solid hydrocarbon in thespace between a graphite resistor element, which has been machined tofit snugly into a refractory protection tube, and the protection tubeinto the resistor assembly heated to a temperature suflicient for therapid decomposition of the hydrocarbon for the formation of carbon or byheating the entire 30 graphite resistor assembly either internally orexternally after the admission of the hydrocarbon until the spacebetween the graphite resistor and the protection tube has beencompletely sealed for the exclusion of atmospheric air.

One example of the operation of my process is given for the sealing of agraphite resistor element in a carborundum protection tube with butaneas the gaseous hydrocarbon. Each end of the graphite resistor, 1%,;inches in diameter and 34 inches long, was threaded into a graphiteterminal 3% inches in diameter and 10 inches long. The assembledresistor and terminals were placed in a carborundum tube 5 inchesoutside diameter, 4 inches inside diameter and 52 inches long and theassembly sealed at both ends. Each graphite terminal had a inch diameteropening which communicated between the external end of the terminal andthe space between the resistor and the protection tube. A metal valvedline was threaded into the external end of each opening. The butane wasadmitted to the space between the resistor and the protection tubethrough one of the valved lines to the pressure of inch of water withthe other valved line closed- A current of 1200 amperes and 10 volts wasapplied to the resistor. This operation was continued until one end ofthe assembly was completely sealed. The butane was then admitted throughthe other valved inlet and the operation continued until the other endof the 5 assembly was sealed. The valved inlet was left in place so thatthe treatment might be repeated as the requirement was indicated by anincrease of resistance in the resistor above normal. The graphiteresistor assembly so prepared was oper- 10 ated continuously in aceramic furnace at a temperature of approximately 1420 C. (2588 F.) fora period of 2283 hours.

It is evident that there are numerous factors which will influenceconditions for the most satisfactory operation of my invention, theactual limits of which cannot be established except by a detailed studyof each set of raw materials and the finished products involved.

Any hydrocarbon may be used for the sealing operation whether it bealiphatic, aromatic or heterocyclic. In fact, any carbon compound whichis susceptible to decomposition at elevated temperature with thedeposition of carbon may be used with equal satisfaction. However, fromthe standpoint of availability and particularly economy it is ordinarilymost desirable to use petroleum, petroleum products or associatedhydrocarbons. The gaseous hydrocarbons which have been found to beparticularly effective are 3 commercial propane, C3Hs and butane, C4H10.Liquid hydrocarbon mixtures, such as naphtha and kerosene, perform theirfunction in the sealing operation in substantially the same manner asthe gaseous hydrocarbon. Liquid hydrocarbon mixtures, such as gas oil,light lubricating oil and heavy lubricating oil are representative ofthe type of this material suitable for the sealing operation. Solidhydrocarbon mixtures, such as parafiin wax and asphalt, perform theirfunction in a manner similar to the liquid hydrocarbon mixtures. I

In the case of the gaseous hydrocarbons and low boiling liquidhydrocarbon mixtures it has been found particularly efiective to admitsuch 1 materials into the space between the resistor and the protectiontube with the assembly already at elevated temperature. In the case ofthe high boiling liquid hydrocarbons and the solid hydrocarbon mixturesit has been found possible to admit the materials into the space betweenthe resistor and the protection tube while the assembly is cool and thenapply heat to the assembly. The heating may be accomplished eitherexternally or internally. In those cases in which the liquid hydrocarbonmixture or the solid hydrocarbon mixture is admitted relatively cool tothe space between the resistor and the protection tube, it is necessaryto leave one 5 valved inlet open with the end of this inlet sealed underoil to provide for a small superatmospheric pressure in the assemblyand, at the same time, to provide for an outlet for the excesshydrocarbon as well as the gaseous decomposition prodl0 uct obtained onpyrolysis of that hydrocarbon remaining in the assembly.

Ordinarily the initial sealing of the assembly is sufficient to secureadequate production for a long period of use. However, under somecircumstances, particularly when it has been necessarily alternatelycooled down and reheated, it may be found necessary to repeat thesealing operation. It has previously been proposed to maintain an inertatmosphere in the space between the graphite resistor element and theprotection tube. This has been found to be particularly expensive whereno provision has been made for sealing the space between the ends of theresistor element and the protection tube. When such space has beensealed in accordance with my invention disclosed herein, it isordinarily not necessary to supply an inert atmosphere to the abovementioned space. However, if it be deemed necessary to maintain a veryslight positive pressure of inert gas on this space after the spacearound the ends of the resistor element have been sealed, this may bedone by supplying inert gas to the inlet mentioned above for use inconnection with the sealing of the resistor assembly when using gaseous35 or highly volatile liquid hydrocarbons. Even under thesecircumstances a very small quantity of inert gas is required.

It will be seen, therefore, that this invention actually may be carriedout by the modification 40 of certain details without departing from itsspirit or scope.

I claim: 1. Process of sealing a graphite resistor into a refractoryprotection tube using a gaseous hydro- 45 carbon, which comprises,heating the graphite resistor assembly to a sufficient temperature toeffeet a rapid pyrolysis of the gaseous hydrocarbon subsequentlyadmitted with the formation of carbon, and admitting the gaseoushydrocarbon into 50 the space between the graphite resistor and therefractory protection tube.

2. Process of sealing a graphite resistor into a refractory protectiontube using a liquid hydrocarbon, which comprises, heating the graphitere- 55 sistor assembly to a sumcient temperature to effect a rapidpyrolysis of the liquid hydrocarbon subsequently admitted with theformation of carbon, and admitting the liquid hydrocarbon into the spacebetween the graphite resistor and the 60 refractory'protection tube.

3. Process of sealing a graphite resistor into a refractory protectiontube using a liquid hydro carbon, which comprises, admitting the liquidhydrocarbon into the space between the graphite resistor and therefractory protection tube, and heating the graphite resistor assemblyto a sulficient temperature to effect a rapid pyrolysis of the liquidhydrocarbon with the formation of carbon.

4. Process of sealing a graphite resistor into a refractory protectiontube using a solid hydrocarbon, which comprises, heating the graphiteresistor assembly to a sufficient temperature to effect a rapidpyrolysis of the normally solid hydrocarbon subsequently admitted in amelted state with the formation of carbon, and admitting the meltedsolid hydrocarbon into the space between the graphite resistor and therefractory protection tube.

5. Process of sealing a graphite resistor into a refractory protectiontube using a solid hydrocarbon, which comprises, admitting the solidhydrocarbon into the space between the graphite resistor and therefractory protection tube, and heating the graphite resistor assemblyto a sufficient temperature to effect a rapid pyrolysis of the solidhydrocarbon with the formation of carbon.

Y 6. Process of sealing a graphite resistor into a refractory protectiontube using a hydrocarbon, which comprises, heating the graphite resistorassembly to a sufiicient temperature to effect a rapid pyrolysis of thehydrocarbon subsequently admitted with the formation of carbon, andadmitting the hydrocarbon in the space between the graphite resistor andthe refractory protection tube.

'7. Process of sealing a graphite resistor into a refractory protectiontube using a hydrocarbon, which comprises, admitting the hydrocarboninto the space between the graphite resistor and the refractoryprotection tube, and heating the graphite resistor assembly to asufficient temperature to effect a rapid pyrolysis of the hydrocarbonwith the formation of carbon.

8. Process of sealing a graphite resistor into a refractory protectiontube using a carbon compound which forms carbon on pyrolysis, whichcomprises, heating the graphite resistor assembly to a suificienttemperature to effect a rapid pyrolysis of the carbon compoundsubsequently admitted with the formation of carbon, and admitting thecarbon compound into the space between the graphite resistor and therefractory protection tube.

9. Process of sealing a graphite resistor into a refractory protectiontube using a carbon compound which forms carbon on pyrolysis, whichcomprises, admitting the carbon compound into the space between thegraphite resistor and the refractory protection tube, and heating thegraphite resistor assembly to a sufiicient temperature to effect a rapidpyrolysis of the carbon compound with the formation of carbon.

ROBERT E. GOULD.

